Aminotransferases perform the transfer of amino groups between amino acids and α-keto acids in a reversible transamination reaction. They catalyze the movement of the amino group from a donor amino acid to an acceptor α-keto acid, producing a new amino acid and a new α-keto acid. The essential cofactor is pyridoxal phosphate (PLP), derived from vitamin B6. PLP forms a Schiff base with a lysine in the enzyme and then forms an external aldimine with the amino acid substrate, allowing the amino group to be removed and reattached through stabilized intermediates. This arrangement enables efficient shuttling of the amino group between molecules. The other options describe different enzyme activities: FAD is a redox cofactor used by dehydrogenases, decarboxylases remove carboxyl groups, and kinases transfer phosphate groups.